Extrageniculate visual pathways and extrastriate visual cortex are important for vision. In light of new knowledge of cortical visual areas based upon mapping and connectivity studies we propose to study the interactions of cortex and midbrain and the roles of specific cortical areas in the learning, retention, and interhemispheric transfer of visual form discrimination and visually guided behavior. In Experiment I we shall make large unilateral lesions of the suprasylvian cortex in cats in which the optic chiasm has been split longitudinally. We shall confirm the observation of deficits in both learning and interhemispheric transfer, and attempt to localize the specific cortical area(s) responsible. We shall then remove the superior colliculus opposite the cortical lesion to test for possible improvement in these visual functions which might be analogous to the "Sprague Effect". In Experiment 2, using split chiasm cats, we shall make smaller suprasylvian lesions that produce no learning deficit by themselves; yet when combined with corpus collostomy result in learning deficits. This implies that cortex contralateral to the lesion "assists" the injured side. We shall then attempt to localize the contralateral area(s) responsible by selective ablation rather than callosotomy and to remove the superior colliculus opposite the original lesion to see if visual function improves. In both experiments 1 and 2 we shall repeat many of the procedures in cats with one optic tract sectioned. Experiment 2 will involve an anatomical study of all cats used in Experiments 1 and 2. Using HRP injected HRP into intact cortical areas, we shall determine whether the cortical lesions had resulted in the retrograde loss of cells in the LP-pulvinar complex whose axons branched and also projected to intact cortex.